The present invention relates generally to a hermetic compressor assembly and, more particularly, to such a compressor assembly having a compressor mechanism mounted in a hermetically sealed housing, wherein it is desired to mount the compressor mechanism to provide an air gap between the rotor and stator components of the compressor motor, and to prevent relative movement between the compressor mechanism and the housing due to torque forces produced by the motor.
A typical hermetic compressor assembly comprises a compressor mechanism and an electric motor situated within a hermetically sealed housing. The electric motor comprises a stator member and a rotatable rotor operably spaced from the stator by an annular air gap. Where the compressor mechanism is a rotary compressor, a cylinder block or main bearing flange is circumferentially mounted to the inside wall of the housing and a crankshaft is journalled in bearings on opposite sides of the cylinder block. One end of the crankshaft is press fit into the center of the rotor which, in turn, is spaced from the stator. In the case of the rotary compressor, the motor stator is circumferentially friction fit against the inside wall of the housing. When mounting the compressor and motor stator within the housing, axial alignment of the rotor and stator is necessary to provide an adequate air gap therebetween.
Another type of prior art compressor mechanism mounted within a hermetically sealed housing is a scotch yoke compressor comprising a crankcase having a circumferential flange member mountable to the interior wall of the housing. In such an arrangement, a crankshaft with a rotor attached thereto is journalled in axially aligned bearings in the housing. Furthermore, the motor stator is mounted to the crankcase member to facilitate axial alignment of the rotor and stator prior to mounting the compressor mechanism assembly within the housing. However, dynamic operation of the motor during starting and stopping imparts a torque force to the crankcase and mounting flange, which tends to cause relative rotational movement between the crankcase and the housing. It is desirable to avoid such rotational movement between the crankcase and housing due to the fact that, for a direct suction compressor wherein a suction tube extends from the housing to the crankcase, damage may result to the suction tube due to stress placed thereon.
Attempts in prior art rotary compressor assemblies to mount the stator and rotary compressor so as to ensure an accurate air gap between the motor rotor and stator have not proven to be entirely satisfactory. One approach is to weld the circumferential surface of the cylinder block or main bearing flange to the interior wall of the housing. Such an approach initially requires an interference fit between the compressor and the housing, which places stress on both the compressor and the housing, especially when welded together. Furthermore, this approach requires close attention to tolerances and tedious alignment during assembly to ensure the proper air gap.
With respect to prior art attempts to secure a frame member within a housing to prevent rotation therebetween, bolts or screws have been used which extend through the housing members into the frame member. This approach, used primarily in other enclosed devices such as pumps, is not suited for hermetic compressor assemblies wherein a pressurized housing is used. More commonly, the crankcase mounting flange is welded to the housing thereby causing stress. Alternatively, relative rotational movement between the crankcase and housing is prevented by a suction line adapter extending between the crankcase and housing. Where rotational forces are taken up by stress on a suction line adapter, a more expensive, robust adapter must be used.
Problems persist in mounting compressor mechanisms within hermetically sealed housings to provide control of the air gap between the motor stator and rotor during compressor assembly. Furthermore, problems are yet experienced with preventing rotation of a compressor mechanism frame within a housing due to torque forces caused by electric motor operating dynamics. Existing mounting methods, primarily welding, place the housing and compressor frame in tension, thereby causing undesirable stress and noise due to compression and expansion of the compressor housing in response to temperature and pressure variations. Furthermore, it is difficult to achieve a satisfactory circumferential weld between a compressor crankcase mounting flange and the inside wall of the compressor housing.